Repairs to a heat exchanger tube often require the plugging of the tube ends when part of the tube becomes corroded or begins to leak. However, before a tube end can be plugged, it is necessary to puncture or sever the body of the tube to evacuate liquid which may be present and create a venting means within the tube. If this is not done, there may be a subsequent pressure buildup in side the plugged tubes when the heat exchanger is returned to service and eventually the plug may blow out, or the tube rupture.
Due to the nature of many types of heat exchangers, access to the tubes is usually restricted; consequently, they must be cut from the inside. Prior to development of the present device, a common procedure for severing tubes to be plugged employed a mechanical fly cutter. One such device is described in U.S. Pat. No. 4,455,746. Such a tool consists of a specially designed pair of cutting bits enclosed within a cutter body. For normal cutting operations the tool is inserted into the tube to be severed, the cutter bits are extended from within the tool by a retractable mandrel, and then the cutter bits are spun in a circular fashion by an air motor. When the bits are fully extended, the tube will normally be completely severed. Afterward, the mandrel is retracted causing the bits to retract within the cutter body thereby allowing removal of the tool.
There are several disadvantages to such a cutting procedure. Using the mechanical fly cutter is a slow and somewhat involved procedure requiring an external driving means such as an air motor and an associated air compressor. Additionally, once the tube has been severed, it is then free to vibrate and possibly to damage surrounding tubes when the heat exchanger is returned to service. The damaged tubes may then require repair as well. Another disadvantage of the cutter device is that metal shavings from the cut tube and dirt may enter the inside of the cutter body where the bits extend, causing the bits to lock in the extended position. When this occurs, it is often difficult or impossible to remove the cutter assembly without damaging or breaking the bits; and thereby necessitating their replacement. Other tools are also known for puncturing tubes to be plugged, but they are often disadvantageous for use in some applications, particularly tubes of small diameter. One such device, described in U.S. Pat. No. 4,730,392, assigned to the assignee of the present application operates on a hydraulic principle. It has been found the hydraulic device may not be well suited to some heat exchangers, particularly ones having smaller tube diameters.
The present invention operates on a mechanical principle and has few moving parts. Thus, the device is quite simple to operate and relatively inexpensive to fabricate.